Short-Range Wireless Communication

ABSTRACT

The present specification describes techniques and apparatus that enable wireless devices to communicate effectively at short ranges. In one implementation, the transmit power of a transmitting device is reduced to permit a receiving device to demodulate a signal.

RELATED APPLICATIONS

This application claims priority to U.S. Provisional Patent ApplicationSer. No. 61/061,977 filed Jun. 16, 2008, the disclosure of which isincorporated by reference herein in its entirety and claims priority toU.S. Provisional Patent Application Ser. No. 61/079,635 filed Jul. 10,2008, the disclosure of which is incorporated by reference herein in itsentirety.

BACKGROUND

Devices that communicate wirelessly often do not communicate effectivelyat short range—e.g., a range less than 1 meter. A user wishing to sink acellular phone with a laptop computer, for example, may find thatneither communicates effectively—or in some cases at all—when thedevices are close to each other.

SUMMARY

A method is described for transmitting, through a network, a link-setuprequest for a device to transmit at a lower-than-nominal power;receiving, through the network and from the device, a link-setupresponse indicating a current transmit power of the device, thelink-setup response having been received at a received power;determining, based on the received power of the link-setup response, adesired data-signal transmit power for the device; and transmitting,through the network, the desired data-signal transmit power to thedevice.

Another method is described for transmitting, from a firstwireless-communication-capable device, a first signal at a first powerand first modulation, the first signal indicating a request to use atransmission medium for a duration of time; and responsive to receivinga response indicating that the transmission medium is free to use forthe duration of time or not receiving a response for a period sufficientto indicate that no potentially interfering device received the firstsignal, transmitting, from the first wireless-transmission-capabledevice, a second signal at a second power, a second modulation, and forless than or equal to the duration of time, the second signaltransmitting data to a second wireless-communication-capable device, thesecond power being a lower power than the first power, and the secondmodulation being different than the first modulation.

A system on chip (SoC) is also described, the SoC configured to receivea link-setup request, the like-setup request requesting transmission ofa data signal at a lower-than-nominal power; transmit a link-setupresponse in response to receiving the link-setup request, the link-setupresponse indicating a current transmit power; receive a desireddata-signal transmit power in response to the link-setup response;transmit a request to use a transmission medium for a duration of time;and transmit, responsive to receiving an indication that thetransmission medium is free to use for the duration of time or notreceiving an indication for a period sufficient to indicate that nopotentially interfering device received the request to use thetransmission medium for the duration of time, the data signal at thedesired data-signal transmit power for less than or equal to theduration of time.

BRIEF DESCRIPTION OF THE DRAWINGS

The detailed description is described with reference to the accompanyingfigures. In the figures, the left-most digit(s) of a reference numberidentifies the figure in which the reference number first appears. Theuse of the same reference numbers in different instances in thedescription and the figures may indicate similar or identical items.

FIG. 1 is an illustration of an example operating environment that isconfigured to enable short-range wireless communication.

FIG. 2 is a graph showing example communication effectiveness relativeto proximity between wireless-communication devices.

FIG. 3 is a method for controlling transmit-power of devices duringshort-range wireless communications.

FIG. 4 illustrates example devices and transmission areas in which alost-node problem can potentially occur in the context of low-powerwireless communications.

FIG. 5 is a method for addressing a potential lost-node problem.

FIG. 6 illustrates an example system-on-chip (SoC) environment.

DETAILED DESCRIPTION

Overview

As noted in the Background above, devices that communicate wirelesslyoften fail to communicate effectively at short range. At short range, asignal receiver in a device may be incapable of demodulating a strongwireless signal. For current wireless LAN communication protocols, suchas IEEE 802.11, the range at which communication becomes less effectiveis at about one meter or closer. At even shorter ranges, such as 0.2meter or less, many devices following this or other communicationprotocols may not be able to communicate at all.

The present specification describes techniques and apparatus that enablewireless devices to communicate effectively at short ranges. In oneimplementation, the transmit power of a transmitting device is reducedto permit a receiving device to demodulate a signal.

In some cases a first device transmitting signals at lower power to asecond device, however, can cause a third device to be unaware of thetransmission between the first device and the second device. Such asituation is referred to herein as a “lost node”—e.g., when a thirddevice (a node) is unaware of another device (the “lost node”), thethird device may transmit a signal even if the lost node is alsotransmitting. The third device may transmit because it is not aware thatother devices are using the same transmission medium. This transmissionby the third device may interfere with the receiver of the receivingdevice or simply obscure the transmission of the “lost node”. To addressthis potential problem as well as for other positive effects, thepresent specification also describes techniques and apparatus thatenable a device to determine that a low-power transmission is being orwill be made. By so doing, devices can communicate effectively at shortrange without interference from other devices.

In the discussion that follows, an example operating environment isdescribed. Example methods are also described that may be employed inthe example operating environment as well as other environments. Thesemethods are followed by an example System-on-Chip (SoC) embodiment inwhich components of FIG. 1 may be embodied. In the discussion below,reference will be made to the environment by way of example only and,therefore, implementations described below are not limited to theexample environment.

Example Operating Environment

FIG. 1 illustrates an example operating environment 100. The exampleoperating environment 100 includes wireless-communication-capabledevices 102, all of which are capable of transmitting and receivingwireless communications, such as those following wireless LAN orBluetooth communication protocols. Devices 102 are shown to include acellular phone 104, a set-top box 106, a television computing device108, a desktop computing device 110, a laptop computing device 112, anda handheld tablet computer 114.

In this example environment, each of devices 102 includes a wirelesstransmitter 116, a wireless receiver 118, and a short-range wirelesscommunicator 120. Wireless transmitter 116 is capable of transmitting awireless-communication signal according to one or more communicationprotocols, such as those for a wireless LAN (Local Area Network) or awireless PAN (Personal Area Network). These protocols may include thoseof the IEEE 802.11 and Bluetooth families of protocols.

Wireless receiver 118 is capable of receiving a wireless-communicationsignal according to one or more communication protocols, such as thosenoted for wireless transmitter 116. Wireless transmitter 116 andwireless receiver 118 may be separate (shown) or combined (often calleda transceiver, not shown) and may be hardware combined with or separatefrom software. Wireless transmitter 116 and wireless receiver 118 arecapable of modulating and demodulating a wireless signal, respectively.

Note that these various wireless-communication protocols may enablecommunication less effectively at short ranges, such as those of lessthan one meter. Even receivers that are relatively capable of handlinghigh-power transmissions (and thus typical short-range transmissions)are often susceptible to some loss of effectiveness at short range.Consider graph 200 of FIG. 2, which shows example communicationeffectiveness relative to proximity between wireless-communicationdevices. Graph 200 shows example communication effectiveness for currentwireless LAN communication protocols of 802.11 and Bluetooth for somedevices. Here the effectiveness of communication drops at about 0.4meter for 802.11 and 0.25 meter for Bluetooth. Effectiveness ofcommunication is shown as throughput in megabytes per second at 202,effectiveness for 802.11 is shown relative to meters proximity at 204,effectiveness for Bluetooth is shown relative to meters proximity at206, with proximity in meters (not to scale) shown at 208.

Short-range wireless communicator 120 (also referred to as “communicator120” for brevity) is capable of enabling a wireless device tocommunicate effectively at short range. Communicator 120 may actindependently or in conjunction with various other entities, such aswireless transmitter 116 and wireless receiver 118. Communicator 120 maybe separate from or integral with other entities of device 102 as well,such as by being firmware integrated into a System-on-Chip (SoC) havingor communicating with wireless transmitter 116 and wireless receiver118.

In environment 100 of FIG. 1, communicator 120 includes a set ofcomputer-executable instructions stored on computer-readable media 122.When executed by one or more processors 124, device 102 acts accordingto those instructions.

Communicator 120 is capable of making decisions and performing one ormore tasks to enable devices to effectively communicate wirelessly atshort range. In some embodiments this also includes addressing a“lost-node” separately from or in conjunction with lowering transmissionpower as described below in the sections entitled “Example Power-controlProcess” and “Lost Node”, as well as elsewhere herein.

Example Power-Control Process

The following discussion describes techniques that may be implementedutilizing the previously described environment. Aspects of the methodmay be implemented in hardware, firmware, software, or a combinationthereof. The methods are shown as a set of blocks that specifyoperations performed by one or more entities and are not necessarilylimited to the orders shown for performing the operations by therespective blocks.

FIG. 3 depicts a method 300 for controlling transmit-power control forshort-range wireless communications. In this example implementation, adata-receiving device, here laptop computing device 112, is attemptingto communicate wirelessly at short range with a data-transmittingdevice, here cellular phone 104. Note that these two devices areexamples of device 102 of FIG. 1, and that both may include the elementsshown for device 102 of FIG. 1 (e.g., communicator 120).

As illustrated, actions performed by a data-transmitting device areshown at 302 and actions of a data-receiving device are shown at 304,both separated by a vertical dashed line. The devices 104 and 112 shownare for illustration purposes, and are not intended to limit the typesof data-transmitting and data-receiving devices. Note also thatcommunications are made between both devices, and thus both transmit andreceive. The data-transmitting device is the device that intends totransmit information over a wireless medium to the data-receiving devicefollowing link setup between the devices, described below.

At block 306, a data-receiving device transmits a link-setup request fora data-transmitting device to transmit at a lower-than-nominal power.The data-receiving device may transmit through various wireless local orpersonal area networks and using various protocols and modulations, suchas those of the IEEE 802.11 family of protocols or the Bluetooth familyof protocols to name a few. The data-receiving device may transmit thelink-setup request using a different modulation or protocol thanintended for future data communications. One such example istransmitting the link-setup request using robust modulation like directsequence spread spectrum techniques (DSSS). Many of these robustmodulations aid in setting up a communication link though they oftenhave lower data throughput than the modulation used in future datatransmissions. The link-setup request may also be sent at alower-than-nominal power to reduce possible interference or saturationby the link-setup request.

At block 308, the data-transmitting device receives the link-setuprequest and responds with a link-setup response indicating a currenttransmit power of the data-transmitting device. In some cases thedata-transmitting device also provides other information in thelink-setup response, such as a link margin associated with thedata-transmitting device. Link margin is a measure of the range ofpowers that the data-transmitting device may effectively demodulate areceived signal.

At block 310, the data-receiving device receives the link-setup responsefrom the data-transmitting device. This link-setup response indicatesthe current transmit power of the data-transmitting device at which thelink-setup response was transmitted. This response is received at aparticular power by the data-receiving device. With this information,the data-receiving device is able to determine a relationship betweentransmit power and received power. As noted in part above, the receivingdevice may also receive the link margin associated with thedata-transmitting device.

At block 312, the data-receiving device determines a desired data-signaltransmit power and transmits this desired data-signal transmit power tothe data-transmitting device. This and other steps of this method may beperformed by short-range wireless communicator 120, as well as wirelesstransmitter 116 and wireless receiver 118, all of which are shown inFIG. 1. Note that both the data-receiving device and thedata-transmitting device may include these entities.

Short-range wireless communicator 120 determines the desired data-signaltransmit power based on the transmit power at which the link-setupresponse was transmitted by the data-transmitting device, the receivedpower of the link-setup response, and a desired data-signal receptionpower. As noted above the link-setup response indicated the transmitpower and the data-receiving device determined the power at whichlink-setup response was received. Communicator 120 determines thedesired data-signal transmission power with this information. In somecases communicator 120 also determines this based on the data-receivingdevice's link margin, hardware capabilities of wireless receiver 118,and/or the modulation that the data signal is intended to betransmitted.

In one implementation, communicator 120 determines the desireddata-signal transmit power according to the following equation:

desiredtransmitPower=TPCresponseTxPower−RSSI_(Rx)+RSSI_(desiredRate)

Here desiredtransmitPower is the desired transmit power at which thedata-receiving device requests that the data-transmitting devicetransmit the data signal. The TPCresponseTxPower is the current transmitpower of the data-transmitting device. RSSI stands for “Received SignalStrength Indication”. The RSSI_(Rx) is the received power of thereceived response. The RSSI_(desiredRate) is the desired received power.The desired power at which the data-signal is received is often based atleast in part on the capabilities and configuration of the wirelessreceiver. Some wireless receivers receive data signals best at aparticular power different from other wireless receivers, eitherindependent of or based on the particular modulation of the data signal.

At block 314, the data-transmitting device receives the desireddata-signal transmit power and transmits a data signal at the desireddata-signal transmit power, which is received at the data-receivingdevice shown at block 316. At this point a link for communication iscomplete for data transmission based on the management transmissionscommunicated at blocks 306 through 312 and part of 314. In some cases,however, the data signal will be received by the data-receiving devicehaving less than a maximum throughput for the modulation at which thedata signal is sent. In such a case the method 300 proceeds alongoptional paths to blocks 318 and 320 as well as repeating some otheractions of method 300.

As noted above, the data-receiving device at block 316 receives signalsat a received power. Communicator 120 may then determine at block 318that the received power has a less-than-maximum throughput for themodulation. Responsive to this determination and based on the receivedpower of the data signal, communicator 120 determines a second desireddata-signal transmit power at block 320. Communicator 120 may do so in amanner similar to the manner in which the first desired data-signaltransmit power was determined.

One difference is that additional information has been gained, such asthe received power of the data signal rather than the received power ofa link-setup response. Responsive to determining this second desireddata-signal transmit power, the data-receiving device transmits thissecond desired data-signal transmit power also at block 320. Thedata-transmitting device may use this information to transmit the datasignal at the second desired data-signal transmit power at block 314.Note that these blocks may be repeated again if the data-receivingdevice determines that the received power is still at aless-than-maximum throughput.

Following the initial link setup, the data-receiving device, if itintends to adjust the transmission power of the data signal, may do soat block 320 using a directed probe response frame, such as those usedin the IEEE 802.11 family of protocols.

This method may be responsive to either the data-receiving device, thedata-transmitting device, or some third-party device determining thatthe nominal transmission power is potentially too high for maximumthroughput between the data-receiving device and the data-transmittingdevice. One such case is when the data-receiving device determines thata data signal or setup signal from the data transmitting device isreceived at a power that does not permit a maximum throughput for themodulation of the signal. The data-receiving device may determine thisthrough interference or saturation at its wireless receiver 118. It mayalso be determined by the data-transmitting device through delays orother information learned from communications from the data-receivingdevice or a third-party device.

The communication link established as part of method 300 can optionallybe maintained, such as with closed-loop or open-loop control. Examplesof open-loop control include ones that determine whether there has beena change in the received data-signal power and, responsive to thischange, change a transmit power of the data-receiving device. Thus,communicator 120 may use an increase or decrease in received power of adata signal from the data-transmitting device to extrapolate that thedata-receiving device will need to increase or decrease its transmissionpower in a similar manner. One case in which this occurs is when adevice moves closer to or further away from the other device. In theexample above a user may move the cellular phone 104 or the laptopcomputing device 112.

In more detail, communicator 120 may adjust transmission power of thedata-receiving device or the data-transmitting device, depending onwhich device this particular communicator 120 resides in, using thefollowing equation:

newtransmitPower=oldtransmitPower−oldRSSI+newRSSI

Here newtransmitPower is the new (second or later) desired transmitpower at which the data-receiving device requests that thedata-transmitting device transmits the data signal. The oldtransmitPoweris the previous transmit power desired and requested. This is also themost-recent previous transmit power if the newtransmitPower is a thirdor later requested power. The oldRSSI is the previous (or in some casesaverage also) received power. The newRSSI is the current received power(or in some cases an average also).

Examples of closed-loop control include periodically re-performing somesteps of the method 300 to determine a new desired data-signal transmitpower or performing these steps responsive to determining a change in athroughput of a data signal. These steps include those performed atblocks 306, 310, and 312 and/or 318 and 320.

Lost Node

As noted in part above, in some cases a device that is transmitting awireless signal may not be noticed by another device intending totransmit a signal. This signal from the other device may interfere withthe signal of the unnoticed device (aka the “lost node”). This potentialproblem is exacerbated when a transmission is made at low power. Toaddress this potential problem, the present specification describestechniques and apparatus that enable a device to determine that alow-power transmission will be made, which permit devices to effectivelycommunicate at short range and often without interference by otherdevices.

FIG. 4 illustrates example devices and transmission areas in which alost-node problem can potentially occur in the context of low-powertransmission. Consider four examples of wireless-communication-capabledevices 102 of FIG. 1. The first two devices are within a low-powertransmission area 402. These two devices are low-power-area transmittingdevice 404 and low-power-area receiving device 406. The second twodevices are within a higher-power transmission area 408. These twodevices are higher-power-area transmitting device 410 andhigher-power-area receiving device 412.

Note that area 402 overlaps with area 408. This overlap illustrates thata device in area 408 may potentially transmit a signal that interfereswith signals in area 402. Such interferences are possible if a device inarea 408 is not aware of low-power transmission in area 402.

The following discussion describes techniques to mitigate this and otherinterferences. These techniques may be implemented utilizing thepreviously described environment of FIGS. 1 and 4 as well as others.Aspects of these methods may be implemented in hardware, firmware,software, or a combination thereof. These methods are shown as a set ofblocks that specify operations performed by one or more entities and arenot necessarily limited to the orders shown for performing theoperations by the respective blocks.

FIG. 5 depicts a method 500 in an example implementation in which adevice can address a potential lost-node problem. At block 502, a deviceintending to transmit at low power transmits a signal requesting atransmission medium for a duration of time. This signal may be senthaving a robust modulation signal to increase the likelihood that adevice (e.g., an Access Point or some device that may transmit) willreceive and understand the transmission. The signal may also or insteadbe sent at a high or nominal power to increase the likelihood that adevice that may not notice a future low-power signal will notice andunderstand this signal.

As noted in more detail below, communicator 120 may determine theduration of time based on how long the data will take to transmit usingthe medium and at a particular low power. This duration may be for aparticular amount or all of the data. These particular amounts may be aslittle as some number of data packets that in total are not sufficientto transmit all of the desired data. This data can be as small as asingle data packet, in which case the duration of time is short. In sucha case the method 500 may be repeated for each packet, packets, or otherparticular amount of data.

Again consider FIG. 4. Here assume that cellular phone 406 intends tocommunicate at low power with desktop computing device 404, such as tosink up cellular phone 406's calendar with desktop computing device404's calendar. Prior to doing so, cellular phone 406 (usingcommunicator 120 and wireless transmitter 116 of FIG. 1) transmits asignal requesting a transmission medium so that the device can transmita signal at low power. Here assume that cellular phone 406 transmitswith wireless transmitter 116 and according to IEEE 802.11, with arobust modulation, and at nominal power. Examples of such a signalinclude a Request To Send (RTS) packet and a Clear To Send-Self(CTS-Self) packet.

At block 504, the transmitting device either receives a response fromone or more third-party devices indicating that the requested medium isfree to use or does not. If no response is received, the device proceedsalong the “No” path to block 506. At block 506, the device waits sometime period sufficient to indicate that no other devices received therequest at block 504 or otherwise indicate that the medium is fee touse. After this wait period, the device proceeds to block 508.

At block 508 the device transmits at low power and for up to about theduration of time requested at block 504. If, however, the devicereceives a response indicating that the requested transmission medium isfree to use, the device follows the “Yes” path to block 508 without await period. A response may include a Clear To Send (CTS) packet fromother devices. Following the transmission at low power at block 508, thedevice may optionally proceed to block 510 to repeat the process. Asnoted in more detail below, the duration of time may be for a particularamount of data. If this amount of data is broken into pieces, or issmall and discrete, such as a packet of data, then multiple pieces andmultiple durations of time may be transmitted and requested.

Continuing the above example, assume that wireless receiver 118 ofcellular phone 406 receives a signal from a device or access point(e.g., tablet computer 410) indicating that the other device or accesspoint is granting the transmission medium. In some cases this signal inresponse to the request may be a CTS frame indicating that the medium isfree to use. When sent from an access point, the response may indicatethat the access point has set its NAV to not use the transmission mediumfor the duration of time. In any of these cases, communicator 120receives this indication (demodulated by wireless receiver 118 andpassed to communicator 120) and proceeds to block 508.

After receiving a response or waiting the period, cellular phone 406transmits at low power (block 508). In this ongoing example, cellularphone 406's wireless receiver 118 receives the response indicating thatthe communication medium will not be used, after which communicator 120permits cellular phone 406's wireless transmitter 116 to transmit at lowpower to desktop computing device 404 for the duration of time. If theduration is for a piece rather than all of the data, the device mayrepeat, following block 510, one or more parts of the method 500.

Note that the method of FIG. 5 may permit devices 404 and 406 tocommunicate at low power without interference from devices 410 and 412.Note also that this method may enable either or both of devices 410 and412 to avoid interference from devices 404 and 406 as well, such as whena low-power transmission from cellular phone 406 may interfere with atransmission (high or low power) from tablet computer 410 that isintended for receipt by laptop computing device 412.

System-on-Chip Example

FIG. 6 illustrates an example System-on-Chip (SoC) 600, which canimplement various embodiments described above. An SoC can be implementedin a fixed or mobile device, such as any one or combination of a mediadevice, computer device, television set-top box, video processing and/orrendering device, appliance device, gaming device, electronic device,vehicle, workstation, and/or in any other type of device that maycommunicate wirelessly in a local or personal area network that mayoperate at short range. Examples of some of these are shown in FIG. 1 at102.

SoC 600 can be integrated with electronic circuitry, a microprocessor,memory, input-output (I/O) logic control, communication interfaces andcomponents, other hardware, firmware, and/or software needed to run anentire device. SoC 600 can also include an integrated data bus (notshown) that couples the various components of the SoC for datacommunication between the components. A device that includes SoC 600 canalso be implemented with many combinations of differing components.

In this example, SoC 600 includes various components such as aninput-output (I/O) logic control 602 (e.g., to include electroniccircuitry) and a microprocessor 604 (e.g., any of a microcontroller ordigital signal processor). SoC 600 also includes a memory 606, which canbe any type of random access memory (RAM), a low-latency nonvolatilememory (e.g., flash memory), read only memory (ROM), and/or othersuitable electronic data storage. SoC 600 can also include variousfirmware and/or software, such as an operating system 608, which can becomputer-executable instructions maintained by memory 606 and executedby microprocessor 604. SoC 600 can also include other variouscommunication interfaces and components, wireless LAN (WLAN) or PAN(WPAN) components, other hardware, firmware, and/or software.

SoC 600 may include wireless transmitter 116, wireless receiver 118, andshort-range wireless communicator 120 (in either or multiple devices asnoted above). Examples of these various components, functions, and/orentities, and their corresponding functionality, are described withreference to the respective components of the example environment 100shown in FIG. 1.

Communicator 120 in SoC 600, either independently or in combination withother entities, can be implemented as computer-executable instructionsmaintained by memory 606 and executed by microprocessor 604 to implementvarious embodiments and/or features described herein. Short-rangewireless communicator 120 may also be provided integral with otherentities of the SoC, such as integrated with one or both of wirelesstransmitter 116 and wireless receiver 118. Alternatively oradditionally, communicator 120 and the other components can beimplemented as hardware, firmware, fixed logic circuitry, or anycombination thereof that is implemented in connection with the I/O logiccontrol 602 and/or other signal processing and control circuits of SoC600.

This specification describes techniques and apparatus that enableshort-range wireless communication by reducing the transmission power ofa transmitting device. This enables a receiving device to demodulate thesignal without being interfered with by a too-powerful transmittedsignal. The techniques described herein also address “lost-node”problems that may arise in lower-power transmissions and in other caseswhere a node is not detected.

Although the subject matter has been described in language specific tostructural features and/or methodological steps, it is to be understoodthat the subject matter defined in the appended claims is notnecessarily limited to the specific features or steps described above,including orders in which they are performed.

1. A method for short-range wireless communication, the methodcomprising: transmitting, through a network, a link-setup request for adevice to transmit at a lower-than-nominal power; receiving, through thenetwork and from the device, a link-setup response indicating a currenttransmit power of the device, the link-setup response having beenreceived at a received power; determining, based on the received powerof the link-setup response, a desired data-signal transmit power for thedevice; and transmitting, through the network, the desired data-signaltransmit power to the device.
 2. The method of claim 1, furthercomprising determining whether communication from the device is receivedat a power level that is too high for maximum throughput at a seconddevice.
 3. The method of claim 1, further comprising: receiving a datasignal from the device, the data signal having a received data-signalpower and having a modulation; determining whether the data signal has aless-than-maximum throughput for the modulation; determining, based onthe received data-power signal and responsive to determining that thedata signal has the less-than-maximum throughput, a second desireddata-signal transmit power; and transmitting the second desireddata-signal transmit power to the device.
 4. The method of claim 3,wherein transmitting the second desired data-signal transmit power tothe device comprises using a directed probe response frame.
 5. Themethod of claim 3, further comprising maintaining a communication linkthrough which the data signal is communicated.
 6. The method of claim 5,wherein maintaining a communication link comprises using open-loopcontrol, the open-loop control being responsive to a change in areceived data-signal power and, responsive to the change in the receiveddata-signal power, changing a transmit power at which communicationswith the device are transmitted.
 7. The method of claim 5, whereinmaintaining a communication link comprises using closed-loop control,the closed-loop control comprising periodically re-performing the stepsof the method for a new desired data-signal transmit power.
 8. Themethod of claim 1, wherein transmitting the link-setup request andtransmitting the desired data-signal transmit power are performed usinga robust modulation.
 9. The method of claim 8, wherein the robustmodulation comprises a direct sequence spread spectrum technique
 10. Themethod of claim 1, wherein transmitting the link-setup request andtransmitting the desired data-signal transmit power comprisestransmitting at lower-than-nominal power.
 11. The method of claim 1,wherein the network is a wireless local area network following acommunication protocol within the IEEE 802.11 family of protocols. 12.The method of claim 1, wherein the network is a wireless personal areanetwork following a communication protocol of within the Bluetoothfamily of protocols.
 13. The method of claim 1, wherein determining adesired data-signal transmit power is further based on a link marginassociated with a data-receiving device.
 14. A method comprising:transmitting, from a first wireless-communication-capable device, afirst signal at a first power and first modulation, the first signalindicating a request to use a transmission medium for a duration oftime; and responsive to receiving a response indicating that thetransmission medium is free to use for the duration of time or notreceiving a response for a period sufficient to indicate that nopotentially interfering device received the first signal, transmitting,from the first wireless-transmission-capable device, a second signal ata second power, a second modulation, and for less than or equal to theduration of time, the second signal transmitting data to a secondwireless-communication-capable device, the second power being a lowerpower than the first power, and the second modulation being differentthan the first modulation.
 15. The method of claim 14, wherein theduration of time is based on an amount of time expected by the firstwireless-communication-capable device to transmit a particular amount ofdata to the second wireless-communication-capable device using thesecond signal at the second power.
 16. The method of claim 14, whereinthe first power is a nominal power of the firstwireless-communication-capable device and the second power is lower thanthe nominal power.
 17. The method of claim 14, wherein the first signalcomprises a Request To Send (RTS) packet or a Clear To Send-Self(CTS-Self) packet.
 18. The method of claim 14, further comprisingreceiving the response indicating that the transmission medium is freeto use, the response received at the first power and the firstmodulation and comprising a Clear To Send (CTS) frame.
 19. ASystem-on-Chip (SoC) configured to: receive a link-setup request, thelike-setup request requesting transmission of a data signal at alower-than-nominal power; transmit a link-setup response in response toreceiving the link-setup request, the link-setup response indicating acurrent transmit power; receive a desired data-signal transmit power inresponse to the link-setup response; transmit a request to use atransmission medium for a duration of time; and transmit, responsive toreceiving an indication that the transmission medium is free to use forthe duration of time or not receiving an indication for a periodsufficient to indicate that no potentially interfering device receivedthe request to use the transmission medium for the duration of time, thedata signal at the desired data-signal transmit power for less than orequal to the duration of time.